The recovery of silver from ore is made more difficult by the presence of manganese and other metals in the ore. Such ore is generally referred to as "refractory ore" since at least 80% of the silver is complexed with manganese. Accordingly, the silver mining industry is constantly attempting to discover and develop processes which can be used to recover the desired silver efficiently from other metal components in mined ore.
Chemical processes for recovery of precious metals are disclosed in U.S. Pat. Nos. 4,740,243, 4,752,332, and 4,765,827. None of these patents disclose processes which come close to the recovery efficiency for silver and manganese achieved with the subject invention process.
Biological recovery of silver and manganese from refractory ore has not been very successful to date. For example, Gupta, A., and H. L. Ehrlich in Jour. of Biotechnology (1989) 9:287-304, used a mold, Penicillium, incubated aerobically, without a chelator with the ore. After 5 weeks incubation, he achieved 23.5% solubfflwtion of Mn and 26.5% solubilization of silver. This result is not considered to be an efficient silver or manganese recovery.
There is no known prior art biological process which provides high enough silver recovery yields to be considered an efficient silver or manganese recovery process.
The biological process of the subject invention is the first known process which yields in excess of 90% silver and manganese recovery from refractory manganiferous silver ore. Thus, the subject process can be termed a landmark achievement in the art of mining manganese and silver.